Directional antenna



Jun 6, 1944. R. R. BRUNNER 2,350,337

DIRECTIONAL ANTENNA Filed nec. 15, 1941 Z3 u /ZZ Patented June 6, 1944 Reed R. Brunner, Baltimore, Md., assigner to United Air Lines, ilnc., a corporation of Dela- 1 Ware Application DecemberV 15, 1941, Serial No. V423,003

(Cl. Z50-11) Claims.

This .invention relates to directional antennas for radio -direction nnders, more particularly to directional antenna arrays .and methods of eliminating undesirable components therefrom, and the invention has for an yobject the provision of apparatus and methods of the above character for rendering more accurate .and reliable the bearing records obtainable by radio direction nders.

Radio direction finders utilizing an Iantenna array of the type to which this invention relates are described and claimed in a copending application of Peter C. Sandretto .and Elmer P. Buckthal. Serial No..403,802, filed .July 24, 1941, entitled Radio direction finder., and in the present application only the antenna array itself will be described. It will be understood, however, that while antenna arrays embodying this invention are particularly applicable to the direction finder systems disclosed in the said Sandretto and Buckthal application, the invention is not limited thereto but may be employed in various other direction nder systems.

vIn antenna arrays comprising spaced loops disposed in substantial face-to-face or coaxial relation, the loops are preferably connected in opposed parallel relation with each other so that the voltages induced in the respective loo-ps will cancel out regardless of variations in the induced voltages so long as the same variations occur .in each loop. Cancellation and zero resultant voltage therefore occur, in so far as the loops themselves are concerned, regardless of variations in the inducing source. The spaced loops, Yas disclosed in the above referred to application, may be mounted on the opposite ends -of a hollow horizontally disposed boom supported for rotation about a substantially vertical medial axis, and the connecting cables or transmission lines from the loops extend through this hollow boom. Voltages induced in these transmission lines by the received radio wave would not ordinarily be canceled out, however, and accordingly the boom is constructed of metallic material to for-rn a shield for the transmission lines, and these lines are transposed kso as to eliminate voltage errors which would otherwise appear in the output of the antenna array.

It is of course known, however, that certain components of the received radio wave will induce currents in a metallic boom of this character, and in order to avoid coupling between the currents flowing in the boom and the antenna loops, it has been proposed to mount the loops on the boom in coaxial relation to each other with the plane of each loop at right-angles to the boom; If the currents flowing in the boom itself were only horizontal, such a right angularrelation would successfully eliminate all coupling, but as a matter of practical necessity the boom which forms the structural support for the loops must have a substantial vertical dimension, and with suc-h a construction it has been .found that eddy currents are set up which now vertically :in the boom and produce` a resultant current iiow -at an angle to the horizontal. With the loops disposed in right angular relation to the boom. coupling of course results, and it is a Yfurther object of this invention to provide an antenna array in which the coupling, due to eddy current ilelds produced by the received radio waveis eliminated, and to provide a simple and reliable method for insuring such elimination.

For a more complete understanding of this invention, reference should now be had to the drawing in which:

Fig. 1 is a somewhat diagrammatic perspective view of an antenna array embodying the present invention;

Fig. 2 is a diagrammatic elevational sectional view of the antenna array ofY Fig. 1 before adjustment in accordance with the present invention; i

Fig. 3 is a vector diagram of the currents which are believed to be induced in the horizontal metallic boom of the antenna array of Fig. 1 by components of the received radio wave; and

Fig. 4 is a view similar to Fig. 2 but showing the antenna array as in Fig. 1 after it has been adjusted in accordance with this invention.

Referring now to the drawing, the invention is shown as embodied in an antenna array comprising a pair of spaced shielded loops l0 and i! having suitable loop conductors I2 and I3 respectively enclosed within tubular shields M `and I5 which are preferably formed of aluminum alloy tubing, the two halves of each shield being separated at the top as shown and suitably insulated as indicated by the reference numeral IS. As shown the loops l0 and Il are mounted adjacent the respective opposite ends of a holloar horizontally extending boom Il through which extend suitable transmission lines i 8 and 49 for connecting the loop conductors I2 and I3 in opposed parallel relation. The boom Il is preferably also formed of aluminum or aluminum alloys and not only provides the necessary mechanical support for the loops I0 and Il, but acts as a shield for the transmission lines I3 and i8 which, as shown, are suitably transposed to elimcomponents 25 and vertical components 25. a Y resultants of the components 2 5 and 26 are illusprovided by -means` of` which `the loops may be secured to the boom in the desired angular relationship thereto. As more fully explained in the above referred to Sandretto and `Buckthall Aelimination of the error-producing components.

f While I have shown a particular embodiment of my invention, it will be understood, of course,

. that I do not wish to be limited thereto since many modifications may'bemade, and I, therefore, contemplate by the appended claims to cover any such modifications as fall Within the true spirit metallic boom mounted in substantially horizonapplication, the boom I'I is supported at substantially its center on a rotatable post 2,2 by. means of which the entireantenna array isrotated in a substantially horizontalplane, and the transmission lines I8 and I9 are connected by suitable conductors 23 to thev direction finder receiver (not shown).

In `lig. 2 the antenna' array is shown with the loops I i! and'II disposed at right angles to the boom II, and, asV heretofore"explained,"'with the loops in this position vcoupling willV occur'between the loops and the currents flowing in the boom itself due to the fact that components of the received radio'wave induce voltages therein. In Fig. 3 there is shown Va vector diagram illustrating the boom currents as comprising horizontal The trated by the' arrowsv 21, and it will be observed that theseresultants extend at an angle a withv respect tothe horizontal.` Coupling with `the loops I0 jand II occurs `dueto the fact` that the loops are notdisposedin right angular relation to Athis resultant current,` and in accordancewith this invention substantially zero coupling is obtained by tilting the loops In and I I to therespective tilted positions shown in Fig. 4, wherein Athe tilt angle is designated by thev letter b. Although the loops Il! and II are shown in the drawingas being tilted inwardly, it will of course be understood variations in the eddy currents may necessitate that the loops be tilted outwardlyinstead.

tIn order accurately to determine the angleof tilt to'be imparted to loops Il] and II so as to insure that substantially zero coupling `with the boom currents will result, it has been found 'preferable to arrange the loops I0 and II in substantially the right angular position shown in Fig. 2 j and to then energize the antenna array from a properly terminated two-wire trar'lsmissionI line `directed substantiallyv parallel toy the boom I'I. vvWith the -antenna array energized solely from this transmissionline, `the conductors v23IV are lconare xedly secured to the boom in the proper and error during actual reception of a radio wave vor by calculation, to `determine the proper angle of tilt which must be imparted to the loo-ps III and II in order to eliminate the effects of error- 'producingcomponenta the above-described method has been found to behighly accurate and is considered the preferable methodof insuring such tal relation for rotation about a Vertical medial axis, a single pair of loops, said loops being positioned on opposite sides of said vertical axis in planes transverse to the longitudinal axis of said boom, means connecting said loops in opposed 'of eddy current elds produced'by components lof a received radio wave and', the tilt angle havling thus been determined, Vthe loopslii and II tilted position. While it may be possible, by trial parallel relation to eachother and means mounting said loops in predetermined oppositely tilted relation to said longitudinal axis.

2. A directional antenna comprising a hollow metallic boom mounted in substantially horizontal relation forrotation aboutV a Vertical medial axis, a single pair of loops, said loops being positioned on opposite sides of said vertical axis in planes transversefto the longitudinalaxis of said boom, meansy connecting said loops in opposed parallel relation to each other and means mounting said loops onsaidV boom inpredetermined oppositely tilted'relationto.theplane of,r rotation of said boom. l l

3y. A directional antenna. comprising a yhollow metallic boomvmounted in substantially horizontal relation vfor rotation about a vertical medial axis, a pair of' loops Vrespectively positioned on opposite sides of said vertical axis` in planes transverse to the longitudinal axis of saidboom, and means mounting vsaid loopsv on said boom with each `loopin substantially zero coupling relation to the elds produced by the eddy currents induced in said ,hollow boom by received radio waves.

4. A directional antennacomprising a hollow metallic boom mounted in. substantiallyhorizontalrelation for roi'jation about a vertical medial ax1s, a single pair'ofshielded loops disposed with one of said loops adjacent each end of said boom 1n a plane transverseto Ithe longitudinal axis of said boom, meansrextending through said hollow boom connecting 'said loops in opposed parallel relation rto each other, and means securing the lower side of each looppto said boom with the upper and lower sides of the loops at right angles to said axis and with the upper side of each loop offset from the Vertical planethroughthe' lower side thereof. i Y

5. Adirectional antenna comprising a hollow metallic boom mounted in substantially horizontalrrelation forrotationqabout a vertical medial axis, a single pair of shielded loopseachhaving a top portion, aA bottom portion and connecting `side portions, means mountingone of said loops adjacent each end of said boom with 'the top and bottom portions at right angles to the. axis of said boom and thefside portions of each loop in tilted relation tofsai'd axisgand means extending through said'hollow boom connecting? saidloops in opposed parallel relation to each other;

6. A directional antenna comprising a hollow metallic boom mounted in substantially horizontal relation for rotation abouta vertical medial axis, and a pair of shielded loops mounted Von said boom with the' top and bottom `vportions' of each loop at right angles to the axis of said boom and the sidesof each loop in tilted relation to said axis in substantially zero coupling relationto the eddy currents induced in said boom by received radio waves.

7. In a directional antenna array of the type comprising a pair of shielded loops disposed in spaced apart substantially face-to-face relation and connected in parallel circuit with each other by transposed transmission lines, the combination of a hollow metallic boom for containing said transmission lines in shielded relation and for supporting said loops for rotation about a medial axis, and means mounting said loops on said boom in such tilted relation thereto as to minimize coupling between said loops and said boom.

8. A rotatable directional antenna array comprising a pair of spaced apart shielded loops, transposed transmission lines connecting said loops in parallel circuit relation with each other, a hollow metallic boom through which said transmission lines extend in shielded relation, said hollow boom being mounted for rotation about a transverse medial axis, and means mounting said loops on said boom adjacent the respective opposite ends thereof and in such tilted relation thereto as to minimize coupling between said loop and said boom.

9. In a rotatable directional antenna array including spaced apart loops mounted in substantially face-to-face relation adjacent opposite ends of a substantially horizontally extending metallic boom, the method of eliminating horizontal components which comprises energizing said antenna array solely from a transmission line disposed substantially parallel to said boom, determining the output of said antenna array, tilting said loops relative to the horizontal axis of said boom to positions in which said output is substantially zero, and securing said loops to said boom in said tilted positions.

10. The method of obtaining a sharp null in th energy received by a rotatable antenna array of the type including spaced apart loops supported on substantially the opposite ends of a rotatable horizontal boom formed of conducting material, which method comprises disposing said loops in substantially face-to-face relation, connecting said loops in opposed parallel Ycircuit relation with each other by conductors extending through and shielded by said boom, transposing said conductors to cancel out the voltages induced therein, energizing said array solely from a transmission line disposed substantially parallel to said boom, determining the output voltage of said array due to said energizing, and tilting said loops to positions wherein said output becomes substantially zero.

REED R. BRUNNER. 

